1. Field of the Invention
Our invention is a specially constructed vent used with explosion proof containers.
2. Description of the Prior Art
Pressure vents of various types are known in the patent art, especially in current Class 220, subclass 88, of the United States Patent and Trademark Office classification system entitled "Metallic Receptacles, Fire Preventing." However, none of this or any other known art can accomplish the results obtained by this invention using the same or similar structure.
The commonly assigned U.S. Pat. No. 4,180,177 to R. J. Gunderman et al was invented by us in conjunction with two other inventors. It discloses a protective outer cover similar to the type we employ with the multilayered material disclosed herein. Its contents is specifically incorporated by reference herein. In considering our present invention, it is vitally important to consider its use and how it interrelates the environment in which used. Essentially it relates to a vent for a protective container which will allow a high flow rate of gases to pass from the container to the outside environment while, at the same time, arresting the flame and cooling its gases before release from the container. The importance of this type of invention becomes self-evident if the container protects electrical controls for mining machines, etc., such as within a coal mine where the air may be laden with an explosive mixture of methane gas.
The patent art discloses many different single layered and several multilayered vent materials. In the mentioned R. J. Gunderman et al patent, the single layered plate 29 forming the porous flame arresting and gas cooling material is made of a porous stainless steel foam material sold under the trade name RETIMET. The same stainless steel foam material is used in the present invention combined with multiple layers of stainless steel screen to achieve the desired results. The known multilayered vent materials use different materials either because they are breathers, and not pressure vents, which allow equalization of pressure on both sides at a slow rate of gas flow or because they are much less effective in providing the results we obtain if at all. For example, U.S. Pat. No. 1,731,406 (F. Bernard) is a safety vent for oil tanks and acts as a breather made up of a flame resistant sponge-like material 10 layered with a fine screen 11. As such, it would not be able to allow the high gas flow rate we do nor would it be able to withstand repeated explosions inside the container. Although similar in its stated desired results, U.S. Pat. No. 2,801,768 (R. B. Immel) does not employ a multilayered vent. It uses for its vent a porous metal filter plate having multitudinous, tortuous, interconnecting pores formed between sintered particles covering the opening. This material would not, according to our testing, provide the gas flow rate needed with the same size vent. Further, the sintered material would have to be protected from damage and clogging.
Other U.S. Pat. Nos. (2,743,035, Fogarty; 3,394,843, Grady, Jr. et al, and 4,149,649, Szego), are also known. None employ the stainless steel foam material we employ in combination with layers of stainless steel screen to achieve the same or similar results we obtained.